In a typical black and white light-sensitive material, silver nitrate is used as a starting material. However, with sudden soaring prices and scarcity of silver in recent years, it has been a serious technical problem in the photographic industry to realize a method which utilizes as little silver as possible to obtain the necessary image density. Hitherto, various methods were proposed to minimize the use of silver.
Examples of the proposal include: (1) A method which increases covering power by a sensitization technique, (2) a method which forms grains into tabular or monodispersed form by use of a grain-adjusting technique and (3) a method which increases the density of the black and white image using a black coupler.
Usable methods for forming a neutral black and white image using a black coupler is disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 42725/1977 featuring use of aminophenol-based coupler, Japanese Patent O.P.I. Publication Nos. 172336/1982, 5732/1983, and 140739/1983 featuring use of resorcinol-based coupler, and Japanese Patent O.P.I. Publication No. 58147/1982 featuring use of the three dye forming couplers, namely, yellow, magenta, and cyan couplers.
Of the above methods, those using aminophenol-based couplers or resorcinol-based couplers provide a relatively nearly neutral black and white image, but do not easily maintain a uniform tone from the low density portion to the high density portion. In the third method, it is difficult to adjust the speeds of the three types of dye forming couplers to produce a black and white image. A slight difference in the speed leads to deteriorated neutrality of image, preventing production of a monochromatic image, and differences in color-fastness during storage produces black and white image with poor gray balance, making this method very difficult to use.
On the other hand, in recent years from the viewpoint of shortening delivery time for photographic prints and improving print productivity, it has been common practice to use rapidly-developable silver halide with a high silver chloride content in the color photographic light-sensitive materials for printing in order to carry out rapid developing in mini-labs. In the mini-labs, the customer can easily obtain a color print from the exposed negative film, but he must wait for a long time to obtain a black and white print because the negative films must be printed in batches in labs specializing in black and white film printing, making it very inconvenient for the customer. For this reason, the photographic industry has been waiting for a light-sensitive material which contains a black-rendering coupler capable of being subjected to processed on the line common to color prints, and which contains silver halide having a high silver chloride content capable of high-speed developing.
Investigations made by the present inventors revealed that although using a high silver chloride content emulsion in conjunction with the foregoing aminophenol-based couplers or resorcinol-based couplers does give a black and white image using a processing solution capable of rapid developing, the obtained image exhibits poor neutrality in that the tone in the low density portion differs from that in the high density portion.